Were the Late Pleistocene climatic changes responsible for the disappearance of the European spotted hyena populations? Hindcasting a species geographic distribution across time

Abstract

This article examines the role of the Late Pleistocene climatic changes in the disappearance of the European populations of spotted hyenas. A species distribution model was built using both current and past environmental requirements of the species. Model projections were made with climatic scenarios provided by the GENESIS 2.0 General Circulation Model (126 ka, 42 ka, 30 ka and 21 ka). Those projections indicate (1) that during the Late Pleistocene warm scenarios spotted hyenas should have been widespread in Europe, and (2) that during the last glacial maximum their potential climatically suitable geographic distribution diminished in size. The decrease in the potential climatic distribution was strictly restricted to Northern Europe. Climatic conditions in Southern Europe during the Late Pleistocene remained within the spotted hyena climatic tolerance. Hence, climate changes could have directly affected the Northern distribution of the species during the last glaciations. However, climate change alone is not sufficient to have caused the disappearance of the spotted hyena populations in Southern Europe. That is, other factors, such as prey abundance or human ecological impacts, in addition to climatic change, are needed to completely account for extinction of the European spotted hyena.

Introduction

At the end of the Pleistocene (approximately 50–10 ka), a worldwide extinction, called the megafauna extinction, affected many of the larger species of mammals (Beck, 1996, Alroy, 1999, MacPhee et al., 2002, Forster, 2003, Barnosky et al., 2004, Louys et al., 2007). In the western Palaearctic region, more than one third of mammalian megafauna genera went extinct (Barnosky et al., 2004), and several widespread and charismatic species disappeared at that time, including Mammuthus primigenius (the woolly mammoth), Homo neanderthalensis (the Neanderthals), Megaloceros giganteus (the Irish Elk), Coelodonta antiquitatis (the woolly rhinoceros) and Crocuta crocuta (the spotted hyena) (Stuart and Lister, 2007). The Pleistocene was characterised by an unstable climate with frequent oscillations between ice ages and warmer interglacial climates (Jackson and Overpeck, 2000). The megafauna extinction coincided temporally with two major events: (1) the last glacial period and the climatic amelioration of the beginning of the Holocene, and (2) Homo sapiens’ expansion out of Africa (dated from 45 to 50 ka (Mellars, 2006)). Therefore, the late Pleistocene extinction is generally considered a regionally contingent event generated by the combined effect of climate changes and human impacts (Barnosky et al., 2004). In the case of Eurasia, climate change would have caused range shifts (Huntley, 1991) that, together with the increase in human populations, could have negatively and severely impacted large mammal populations (see Nogués-Bravo et al., 2008).

C. crocuta (the spotted hyena) is one of the large mammals that became extinct in Europe at the end of the late Pleistocene. Prior to their extinction, spotted hyenas were present in Europe for at least 1 million years (Garcia and Arsuaga, 1999, Carrión et al., 2001). Fossil remains of the species suggest that during the Pleistocene they were present all over the continent from the Iberian Peninsula to the Urals (Testu, 2006). Some authors have assigned the European spotted hyena fossil remains to a subspecies of the African spotted hyenas (Crocuta crocuta spelaea, Crocuta crocuta intermedia; see Kurtén, 1957, Kurtén, 1968, Werdelin and Solounias, 1991), while others consider them a distinct species (C. spelaea; Soergel, 1937, Musil, 1962, Markova et al., 1995). Recently, the taxonomic status of the Pleistocene European spotted hyenas was revised using ancient DNA. That analysis confirmed the existence of genetic flow between the African and Eurasian populations during the Pleistocene (Rohland et al., 2005). Thus, similar to the situation for plants, it appears that the dominant response of mammal species during Quaternary climatic oscillations was extinction or range shift, not evolutionary change (Willis and Niklas, 2004). In this paper, we considered the European spotted hyena fossil remains as belonging to C. crocuta following Rohland et al. (2005). First, we estimate the climatic niche of this species from distributional data (the set of a priori favourable climatic conditions for the species) using the climatic information generated by the GENESIS 2.0 General Circulation Model (Pollard and Thompson, 1997). Second, we geographically projected this estimated niche in Europe for five temporal scenarios (126 ka, 42 ka, 30 ka, 21 ka and present) to ascertain the possible role of Pleistocene climatic changes on the potential distribution of European spotted hyenas. Climate is frequently considered a key factor in explaining the geographical distribution of species at large spatial and temporal scales (Bowyer et al., 1998, Geffen et al., 2004). Macroecological and biogeographical studies based on current data support the hypothesis that climate controls or at least strongly contributes to explaining the distributions of species (Currie, 1991), and many paleontological analyses also highlight the relevance of climate. For example, the Plio-Pleistocene crisis (Kostopoulus et al., 2007) or species replacements during the Pleistocene are usually related to climatic changes (Cardoso, 1996, Barry et al., 2002, Coard and Chamberlain, 1999, Sommer and Benecke, 2005). In this article, we address the question of whether climatic change alone was sufficient to account for the extinction of spotted hyenas in Europe. We test whether extinction of the spotted hyena in Europe was related to a decrease in climatically favourable area during the Pleistocene. Finally, we discuss methodological influences on model predictions when using paleontological data.